JPH06166518A - Production of fine particle of ba@(3754/24)snxti1-x)o3 solid solution - Google Patents

Abstract

PURPOSE:To obtain fine particles of a Ba(SnxTi1-x)O3 solid solution having high uniformity and activity by carrying out the heat treatment at a lower temperature than that in a conventional solid-phase reactional method. CONSTITUTION:In the method for producing fine particles of this invention, an Sn compound or its hydrolyzate is mixed with a Ti compound or its hydrolyzate at a prescribed ratio and a Ba salt is then added and made to react with the resultant mixture in a strongly alkaline aqueous solution at a temperature near the boiling point to wash the formed precipitate with water or warm water. Thereby, alkali ions such as K<+>, Li<+> or Na<+> are sufficiently removed and the obtained precipitate is filtered and dried to afford mixed fine particles of BaTO3 fine particles with BaSn(OH)6 fine particles. The obtained mixed fine particles are then heat-treated at, e.g. 1260 deg.C for 3hr to provide the objective fine particles of a Ba(SnxTi1-x)O3 solid solution [0<(x)<1].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing Ba (SnxTi _1-x ) O ₃ solid solution fine particles using mixed fine particles of BaTiO ₃ and BaSn (OH) ₆ which are one type of dielectric material.

[0002]

2. Description of the Related Art In recent years, a manufacturing method for making fine particles of a ceramic material has been studied from various angles, and one application of the finely divided ceramic material is application to a capacitor. With the miniaturization and higher density of electronic products, capacitors are also smaller, like other electronic parts.
Lighter weight, larger capacity, and higher resistance to high frequencies are required. Therefore, in the ceramic capacitor, it is necessary to make the dielectric material fine particles in order to make the thickness of the ceramic layer thin and uniform. In addition, by making the particles fine, it becomes possible to keep the sintering temperature low. Besides this,
As a raw material for an electrostrictive material, a piezoelectric material, a transparent ceramic material, etc., a material having a small particle size and a uniform material is expected in order to improve, for example, sinterability and temperature characteristics.

[0003]

As one of such dielectric materials, a solid solution of barium titanate and barium stannate Ba (SnxTi _1-x ) O ₃ (hereinafter abbreviated as BSTx, numeral x is Sn). Mol%, 0 <x <1)
In order to obtain this solid solution, BaCO ₃ and Sn are conventionally used.
Solid-state reactions using O ₂ and TiO ₂ or BaTiO ₃ and BaSnO ₃ as raw materials have been performed. When the BST solid solution obtained by this solid-phase reaction is made into fine particles, it is unavoidable that impurities such as Al ₂ O ₃ are mixed in the powdering step after calcination. In addition, there are problems such as uneven molding and increased pores after sintering due to the nonuniform particle size of the fine powder of solid solution. Furthermore, it cannot be said that the solid solution fine particles thus obtained have a high solid solution homogeneity, and a compositional variation locally, that is, a portion having a large content of Sn or Ti appears. This is because the particle size of the fine particles after calcination is non-uniform and relatively large, and the diffusion state of the fine particles of Sn and Ti is different. As a result, in terms of dielectric properties, there are problems such as deterioration of the expected diffusion phase transition profile, and there is much room for improvement. In addition, at present, it is difficult to obtain single-phase BST solid solution particles by a solid phase reaction, and it is necessary to set the temperature to 1500 ° C. or higher depending on the composition. This is a serious problem in obtaining a single phase and in utilizing the dielectric properties of the solid solution particles.

Recently, various attempts have been made to improve these problems, and one of them is the metal alkoxide method. The metal alkoxide refers to a compound in which a hydrogen atom of alcohol is substituted with a metal. As a method for synthesizing Ba (ZrxTi _1-x ) O ₃ by this metal alkoxide method, for example, there is one disclosed in Japanese Patent Publication No. 58-2220, and Ba (SnxTi _1-x ) by this method
No report has been made yet regarding a synthetic example of O ₃ . However, the metal alkoxide, which is an organometallic compound used in this synthetic method, has many problems in practical use in that the price is much higher than that of the raw material used in the usual solid-phase reaction method.

On the other hand, the applicant of the present invention has proposed a method for synthesizing BaTiO ₃ (Japanese Patent Application No. 57-147226) and BaSn (OH) ₆
(Japanese Patent Application No. 58-49765) was proposed, but a method is conceivable in which the solid solution fine particles are obtained by separately synthesizing the two and then mixing them. However, according to this method, it is not simple to mix in the target ratio. That is, since both compounds have a weight loss like adsorbed water at the time of synthesis, they cannot be immediately mixed only by weighing. It is necessary to perform heat treatment once and examine the weight loss to find out what percentage of the unheated matter is effective.

The present invention provides a method for producing Ba (SnxTi _1-x ) O ₃ solid solution fine particles which can solve the above problems.

[0007]

In the present invention, first, a Sn compound or a hydrolysis product thereof and a Ti compound or a hydrolysis product thereof are mixed at a predetermined ratio, and then Ba salt is added to the mixture to give a strong alkalinity. The reaction is carried out in an aqueous solution at a temperature near the boiling point, and the formed precipitate is washed with water or warm water to sufficiently remove alkali ions such as K ⁺ , Li ⁺ , Na ^{+, and the} like, and the BaTiO ₃ fine particles and BaSn are removed by filtration and drying. Fine particles mixed with (OH) ₆ fine particles are obtained.
Next, BaTiO ₃ and BaSn obtained by the above operation
Ba (SnxTi _1-x ) O ₃ solid solution particles can be obtained by subjecting the mixed particles of (OH) ₆ to heat treatment.

Here, the Sn compound is SnC.
l ₄ , Sn (NO ₃ ) ₄ , Sn (SO ₄ ) ₂ , Sn (S
O ₄₎ as a ₂ · 2H ₂ O, etc., also hydrolysis products of Sn compounds, NH ₄ OH aqueous solution thereof, LiOH, N
The one hydrolyzed with an alkaline solution such as aOH or KOH can be used. However, when sulfate radical SO ₄ ²⁻ is present, it is necessary to remove the sulfate radical by sufficiently repeating decantation and filtration after hydrolysis. In addition, it is a soluble stannate such as Na ₂ SnO ₃ .3H ₂ 0, K ₂ Sn
O ₃ · 3H ₂ O or the like may be used.

Ti compounds include TiCl ₄ , Ti
(SO ₄ ) _{2 and the} like, and as the hydrolysis product of the Ti compound, a solution obtained by hydrolyzing the aqueous solution with the above alkaline solution can be used. However, Ti (SO ₄ )
_When using ₂ , it is necessary to remove the sulfate radical SO ₄ ^2- , so that it is hydrolyzed once with alkali to produce TiO ₂ · n.
Make H ₂ O, use after decantation and filtration.

The Ba salt includes Ba (NO ₃ ) ₂ and Ba.
(OH) ₂ , BaCl ₂ , Ba (CH ₃ COO) _{2 and the} like can be used. Moreover, you may use these hydrolysis products. BaTiO ₃ and BaSn (OH)
_As reaction conditions when synthesizing the mixed fine particles composed of ₆ ,
The pH of the strongly alkaline aqueous solution is 13.0 or higher, preferably 13.2 or higher, and the reaction temperature is 80 ° C. or higher, preferably 90.
℃ or more, the reaction time is 5 minutes or more, preferably 30 minutes or more,
The molar ratio of Ba / (Sn + Ti) is in the range of 0.7 to 2.0, preferably around 1.0.

The heat treatment conditions applied to the mixed fine particles of BaTiO ₃ and BaSn (OH) ₆ differ depending on the Sn content of the BST solid solution fine particles, but if the Sn / Ti molar ratio is close to 1, 1260 ° C. It may be about 1350 ° C., and if the Sn / Ti molar ratio is ∞ or close to 0, it is 1
It is necessary to raise the temperature to about 400 ° C to 1460 ° C.
However, this heat treatment condition is applied when the purpose is to obtain single-phase BST solid solution particles, and when used for other purposes, the heat treatment temperature may be set according to the purpose of use.

[0012]

EXAMPLES The present invention will be described below based on examples.

Example 1 About 200 g of TiCl ₄ was added to ice water with stirring to prepare an aqueous solution, which was then transferred to a volumetric flask to adjust the volume to 1
000 cc. Then, take a portion from this solution,
Ammonia water is added in excess to precipitate TiO ₂ . After subjecting this precipitate to a heat treatment at about 1000 ° C., it is weighed to determine the exact concentration of the TiCl ₄ standard solution in the volumetric flask (in this case 0.9595 mol / l). On the other hand, as an Sn compound in which the B site of an ABO ₃ perovskite type compound is replaced with Sn, BST50
(That is, Ba (Sn _0.5 Ti _0.5 ) O ₃ ) so that 30.67 ml of the above TiCl ₄ standard solution and Na ₂ are obtained.
After accurately collecting 7.848 g of SnO ₃ .3H ₂ O in a beaker, 15.38 g of Ba (NO ₃ ) ₂ was further added and dissolved. Next, a previously adjusted 5N-KOH solution was added to adjust the pH to 13.6 to obtain a white turbid liquid having a total solution amount of 400 ml. The solution is agitated while boiling and aged for about 7 hours. Use warm water for the white precipitate formed after aging 1
Impurities such as alkali ions are removed by repeating decantation about zero times. Next, this precipitate is separated by filtration and dried at 90 ° C. for one day to obtain a fine particle powder.

The fine particle powder obtained by the above operation was analyzed by X-ray diffraction (copper target, Niken filter). As a result, the X-ray diffraction pattern was 5-0 on the ASTM card.
626 (BaTiO ₃ ) and 9-53 (BaSn (OH))
_{A value} corresponding to the synthetic pattern of ₆ ) was obtained. Therefore, this fine particle powder is composed of BaTiO ₃ fine particles and BaSn particles.
It was confirmed that the mixture was a mixture of (OH) ₆ fine particles. The mixed fine particles are stoichiometrically composed of BaTiO ₃ : BaSn.
(OH) ₆ = 1: 1. Scanning electron micrographs of the mixed fine particles are shown in FIGS. 1 and 2 (enlarged photograph). 20
˜30 μm needle crystals are BaSn (OH) ₆ ,
Fine spherical crystals of 0.1 to 0.2 μm are BaTiO ₃ .

Next, the mixed fine particle powder is heat-treated at 1260 ° C. for 3 hours. The fine particle powder thus obtained is analyzed by X-ray diffraction in the same manner as above, and the results are shown in FIG. This X-ray diffraction pattern is based on BaTiO ₂ and BaSn.
Its peak appeared at the diffraction position estimated from the X-ray diffraction pattern of O ₃ , confirming that it was a single phase of BST5O. In addition, for reference, an X-ray diffraction pattern of a product subjected to heat treatment at 1260 ° C. for 3 hours using a conventional solid-phase reaction method is shown in FIG. This one is Ba
It has two phases of SnO ₃ and Ba (SnxTi _1-x ) O ₃ , and it was confirmed that the reaction is still in progress unlike the product of the present invention. The conventional BST 50 is created as follows. BaCO ₃ and TiO ₂
And SnO ₂ in a molar ratio of Ba: Ti: Sn = 1: 0.5:
The amount is adjusted to 0.5 and the total amount is adjusted to 0.1 mol. Then, the mixture is put into a polyethylene bottle, and about 30 cc of water is further added. Next, after mixing and crushing for 15 hours in a ball mill, 1
BST50 is obtained by heat treatment at 415 ° C. Therefore, according to the solid-phase reaction method, 1
A high temperature of 50 ° C or higher is required.

Example 2 A TiCl ₄ standard solution (0.9595 mol / l) prepared in the same manner as in Example 1 is prepared. Next, about 26
After adding 0 g of SnCl ₄ to ice water while stirring to make an aqueous solution, the solution was transferred to a volumetric flask and the volume was adjusted to 1000
Let cc. Then, as in the case of TiCl _4, a part of this solution is sampled and ammonia water is added in excess to add S.
After the nO ₂ was precipitated, it was heat-treated at 1000 ° C. for about 3 hours and weighed to determine the exact concentration of the SnCl ₄ standard solution (in this case, 0.9015 mol / mol).
was 1). Then, to obtain BST50, S
1 solution of Ba (NO ₃ ) ₂ was added to a solution containing 32.64 ml of nCl ₄ standard solution and 30.67 ml of TiCl ₄ standard solution.
After dissolving 5.38 g, the pH is adjusted to 13.7 with NaOH solution. The solution is agitated while boiling and aged for about 6 hours. Impurities such as alkali ions are removed by repeating decantation about 10 times using warm water on the white precipitate formed after aging. Next, this precipitate is separated by filtration and dried at 90 ° C. for one day to obtain a fine particle powder.

The fine particle powder obtained by the above operation was analyzed by X-ray diffraction, and the results were as follows: BaTiO ₃ fine particles and Ba
It was confirmed that the mixture was a mixture of Sn (OH) ₆ fine particles. Further, according to the scanning electron micrograph of this fine particle powder, fine particles having a shape similar to those in FIGS. 1 and 2 could be observed.

Next, FIG. 5 shows the results of examining the change in lattice constant by subjecting this fine particle powder to heat treatment for 3 hours at different temperatures. From this graph, it was found that the two-phase mixed state continued until 1260 ° C., but when it exceeded 1260 ° C., it became a single-phase BST50. From this phase change state, the lattice constant of BaSnO _{3 of} the first phase does not change up to about 1260 ° C., while the BaTiO _{3 of} the second phase of BaSnO ₃ does not change at all.
Due to the diffusion of Sn, the lattice constant gradually changes from around 1000 ° C., and Ba (Snx
It is clear that the Ti _{x of} Ti _1-x ) O ₃ tends to increase. This proves that BaSnO ₃ unilaterally diffuses during the diffusion phenomenon due to the heat treatment.

Example 3 BaTiO ₃ and BaSn synthesized in the same manner as in Example 1
A mixed fine particle powder composed of (OH) ₆ is prepared. next,
By subjecting this powder to a heat treatment at 1400 ° C., BS
T solid solution fine particles are obtained. On the other hand, BST solid solution particles obtained by the conventional dry solid-phase reaction method (heat treatment temperature 1430 ° C.) are also prepared. Then, with respect to both of them, Ni ^{filter, 1 0 DS-0,15mm RS-} 1 0 SS slit condition and 1/4 ° / min scan rate, the time constant 1 sec conditions with the plane index of (100) ( 200) (300) (40
X-ray measurement was performed on the diffraction pattern of 0). on the other hand,
The integral width β of only the BST solid solution sample using Si powder as a standard sample was calculated by the Jones method to give a non-uniform strain η β cos θ / λ-sin θ / λ
A graph obtained by plotting is shown in FIG. The straight line A shows the solid solution fine particles according to the present invention, and the straight line B shows the solid solution fine particles obtained by the solid phase reaction method. In this graph, the slope of the straight line is 2η
Since (η = Δd / d), it can be seen that the BST solid solution fine particles obtained by the present invention having a very small inclination have less fluctuation of the lattice constant, and therefore the composition variation is very small. On the other hand, in the case of BST solid solution fine particles produced by the solid-phase reaction method, the composition variation is 0.400 <x <
It is 0.600, which shows that the composition variation is extremely large.

Example 4 TiCl ₄ and Sn prepared in the same manner as in Examples 1 and 2
Using a standard solution of Cl ₄ , BST 10, 20, 30,
An appropriate amount of Ba is added and mixed so as to obtain 40, 50, 60, 70, 80 and 90, and then reacted in a strongly alkaline aqueous solution to obtain 9 kinds of fine particle powders.
The X-ray diffraction patterns obtained for these fine particle powders are all Ba
It was confirmed that the particles were mixed fine particles composed of TiO ₃ and BaSn (OH) ₆ . Next, in order to obtain single-phase BST solid solution fine particles, 1 is added to the above 9 kinds of mixed fine particles.
It heat-processed at 460 degreeC for 3 hours. However, depending on the composition, solid solution fine particles can be obtained at a temperature much lower than this temperature, but those having a large Sn content and BaTiO 3
High heat treatment temperature is required for the composition very close to the ₃ side. FIG. 7 shows the result of calculating the lattice constant of each BST solid solution fine particle prepared in this way using the high angle side (90 ° or more) of the Nelson-Riley extrapolation function.
Shown in. The lattice constant of the BST solid solution microparticles wet-synthesized according to the present invention closely follows the Vegard side.
It should be noted that when obtaining such results by the conventional solid-phase reaction method, it is obvious that a very high processing temperature of 1500 ° C. or higher is required.

Example 5 A scanning electron micrograph of BST50 solid solution fine particles obtained by heat-treating the mixed fine particles according to the present invention prepared in the same manner as in Example 1 at 1260 ° C., which is the lowest temperature at which a single phase is obtained. 8 and FIG. 9 (enlarged photo). In addition, the minimum temperature of the solid phase reaction method shown in Example 1 is 141, which is a single phase.
Scanning electron micrographs of BST50 solid solution particles obtained by heat treatment at 0 ° C. are shown in FIGS. 10 and 11 (enlarged photo). As is clear from FIGS. 8 to 11, the BST solid solution fine particles produced by the present invention have a particle size of 1 to 2 μ and are highly uniform, whereas the BST solid solution fine particles produced by the solid phase reaction method have two It can be seen that the particle size is 0.5 to 5.0 μm, which is non-uniform, from the subsequent aggregation to the sintering stage. These comparisons demonstrate that the wet synthesis method according to the present invention is superior to conventional solid phase reaction methods.

[0022]

As described above, according to the present invention, BaT
After wet synthesis of mixed fine particles of iO ₃ and BaSn (OH) ₆ , BST solid solution fine particles can be obtained at a heat treatment temperature lower by about 150 ° C. as compared with the conventional solid-phase reaction method.
Since the BST solid solution fine particles have high uniformity in particle size, they are highly active and at the same time have high sinterability at low temperatures. Further, since they are high-purity fine particles with very little composition fluctuation, they have excellent dielectric properties. Furthermore, since the diffusion of Sn and Ti in the mixed fine particles is high, calcination is not required,
It is also possible to immediately start the main firing with one heat treatment.
This is because BaSn (OH) ₆ once turned into a skeleton during the heat treatment and became amorphous, and BaSn (OH) ₆ formed next was formed.
It is presumed that this is because the O ₃ fine particles unilaterally diffuse into the BaTiO ₃ fine particles. According to the present invention, since it can be obtained in a crystalline state during the synthesis of the mixed fine particles, filtration and the like are easy and the productivity is high. In addition, since the starting material is inexpensive, it is very economically advantageous as compared with the same wet synthesis method such as the metal alkoxide method.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of mixed fine particles of BaTiO ₃ and BaSn (OH) ₆ .

FIG. 2 is a scanning electron microscope photograph (enlarged photograph) of mixed fine particles composed of BaTiO ₃ and BaSn (OH) ₆ .

FIG. 3 is a diagram showing an X-ray diffraction pattern of BST50 synthesized according to the present invention.

FIG. 4 is a diagram showing an X-ray diffraction pattern of BST50 synthesized by a solid-phase reaction method.

FIG. 5 is a characteristic diagram showing a relationship between a heat treatment temperature and a lattice constant in the present invention.

FIG. 6 shows β cos θ / λ-sin θ for non-uniform strain
It is a characteristic view which measured / λ.

FIG. 7 is a characteristic diagram showing the relationship between the composition of BST solid solution particles and the lattice constant.

FIG. 8 is a scanning electron micrograph of BST50 according to the present invention.

FIG. 9 is a scanning electron micrograph (enlarged photograph) of BST50 according to the present invention.

FIG. 10 is a scanning electron micrograph of BST50 synthesized by the solid-state reaction method.

FIG. 11 is a scanning electron micrograph (enlarged photograph) of BST50 synthesized by the solid-state reaction method.

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[Procedure amendment]

[Submission date] December 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing the particle structure of mixed fine particles of BaTiO ₃ and BaSn (OH) ₆ .

FIG. 2 is a scanning electron microscope photograph (enlarged photograph) showing a particle structure of mixed fine particles composed of BaTiO ₃ and BaSn (OH) ₆ .

FIG. 3 is a diagram showing an X-ray diffraction pattern of BST50 synthesized according to the present invention.

FIG. 4 is a diagram showing an X-ray diffraction pattern of BST50 synthesized by a solid-phase reaction method.

FIG. 5 is a characteristic diagram showing a relationship between a heat treatment temperature and a lattice constant in the present invention.

FIG. 6 shows β cos θ / λ-sin θ for non-uniform strain
It is a characteristic view which measured / λ.

FIG. 7 is a characteristic diagram showing the relationship between the composition of BST solid solution particles and the lattice constant.

FIG. 8 is a scanning electron micrograph showing the grain structure of BST50 according to the present invention.

FIG. 9 is a scanning electron micrograph (enlarged photograph) showing the particle structure of BST50 according to the present invention.

FIG. 10: Particles of BST50 synthesized by solid-phase reaction method
It is a scanning electron micrograph showing a structure .

FIG. 11: BST50 particles synthesized by solid-state reaction method
It is a scanning electron microscope photograph (enlarged photograph) showing a structure .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hidemasa Tamura 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (1)

[Claims] 1. BaTiO ₃ and BaSn (obtained by mixing a Sn compound or its hydrolysis product with a Ti compound or its hydrolysis product, adding Ba salt, and reacting in a strongly alkaline aqueous solution. OH) ₆
Characterized in that a heat treatment is applied to the mixed fine particles of B
a (SnxTi _1-x ) O ₃ (0 <x <1) solid solution fine particles.